Fossils show earliest mammals that lived in trees and below ground

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The fossils of the Agilodocodon scansorius is shown at left, found in lake sediments and the Docofossor brachydactylus at right.

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Early mammals lived in trees and underground even as dinosaurs roamed the earth, according to new research

Two fossils show creatures resembling a monkey and a mole

Discovery shows mammals were able to adapt despite competition from dinosaurs

Beijing (CNN)Prehistoric fossils discovered in China are believed to be the earliest known mammals to have lived in trees and below ground.

The newly found creatures were tiny -- the size of a shrew -- and are believed to have roamed roughly 165 million years ago, at the same time as dinosaurs. The tiny creatures resembled moles and monkeys.

This is an illustration of Agilodocodon and Docofossor. The skeletal features of Agilodocodon, left, suggeset it was an agile and active arboreal animal. The skeletal features of Docofossor, right, suggest it lived in burrows and fed on worms and insects.

According to the new research, the tree-dwelling creature -- Agilodocodon scansorius -- had curved horny claws and spade-like front teeth that allowed it to gnaw at bark -- an adaptation seen in some modern monkeys.

The other -- Docofossor brachydactylus — had shovel-like paws and a skeleton structure and body proportions "strikingly similar" to the modern African golden mole. It lived in burrows and fed on worms and insects.

"These new fossils help demonstrate that early mammals did indeed have a wide range of ecological diversity," said Zhe-Xi Luo, a professor at the University of Chicago and an author of both papers. "It appears dinosaurs did not dominate the Mesozoic landscape as much as previously thought."

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Fossils of the two species were discovered in 2011 and 2012 by scientists from Beijing Museum of Natural History and are now stored in the museum.

Early mammals were once thought to have limited ecological opportunities to diversify, but the discovery of these two fossils suggest that ancestral mammals adapted to wide-ranging environments despite competition from dinosaurs.

"We now know that they (early mammals) could not only climb trees, but also dig holes," said Ji Qiang, a researcher of the Institute of Geology at the Chinese Academy of Geological Science and one of the report's authors.

"It means that they occupied a variety of ecological niches millions of years ago."